The invention provides rotary bell cup atomizers generally useful in the coating of substrates. Rotary bell cup atomizers are commonly used in coating operations such as, for example, the painting of vehicle body parts. These coating operations are carried out, in the main, by either robotically mounted and controlled atomizers or by hand-held spray gun atomizers. Both coat various work-pieces by operation of bell cup rotating atomizers affixed thereto.
Rotary atomizers are used in liquid based paint coating operations and bell cup rotary devices are also used in powder coating operations. The invention herein described and claimed can be useful in both types, either robotically or machine mounted, or applied via hand-held spray gun.
Rotary atomizers which are used in coating various substrates employ centrifugal forces generated by a rotating bell cup to atomize paint supplied thereto. In a conventional process, pressurized air is directed as an axially-extending shroud around the periphery of the atomized paint and this shroud controls the disposition pattern of paint particles deposited on the work-piece. Electrostatic charging may be used to assist in attracting the atomized particles to the substrate, all of which is known.
Examples of state-of-the-art rotary bell cup atomizers are found in prior patents of one or both of the named inventors herein, specifically in U.S. Pat. Nos. 7,056,397, 6,676,049, 6,341,734, 6,053,428 and 5,862,988.
In the spray painting of vehicle bodies, for example, improvements in application methods continue, specifically in enhancements to the spray pattern geometry produced on the substrate, a result of which is controlled by the velocity and direction of the shaping air flowing axially and peripherally about the outside edge of the bell cup and enveloping the sprayed coating exiting the cup.
The quality of the final coating is dependent upon many variables in addition to the velocity and direction of the atomized paint particles, among them being the electrostatic effect in carrying the atomized charged particles to the grounded substrate. In addition, the deposited film quality and aesthetics of the applied coating are dependent upon surface irregularities, protrusions, and edges in and on the surface to be coated. Controlled shaping air cited above plays an important role in producing an acceptable, and optimal, coated final product.
An example of a method for controlling the spray pattern applied by a rotary atomizer is found in U.S. Pat. No. 7,611,069 B2 (2009). That reference is directed to an atomizer having a spray head which includes an annular shaping air ring having a plurality of nozzles for controlling the spray pattern, wherein each nozzle has a right-handed triad orientation having a base coordinate system that is placed on the longitudinal axis of the nozzle in a specified orientation. The reference is said to optimize the control of shaping air to create a stable, focused pattern that minimizes robot speed while maintaining high transfer efficiency.
U.S. Pat. No. 4,601,921 (1986) discloses a method carried out by centrifugally dispersing coating material in an annular pattern about an axis and directing a conical sheath of air forwardly through the pattern and toward a confluence on the axis with sufficient velocity to effect turbulent mixing of particles of the coating material, so that the coating material is atomized and deposited on the workpiece in a film of substantially uniform thickness. The method is said to impart a swirl component to the sheath of air to cause enlargement of the spray pattern which emerges from the confluence. The method is carried out by a rotary spray head having a forward rim for centrifugal dispersion of coating material and a vortex plenum surrounding the head provided with an annular discharge slit for projecting a conical sheath of air around the rim to direct the coating material forwardly and inwardly, and controls for the plenum airflow include an air input for air moving in a forward flow direction and another air input for tangential airflow to impart a swirl moment to the sheath of air.
A more recent patent, U.S. Pat. No. 9,833,797B2 (2007), discloses electrostatic coating apparatus which includes an air motor, a rotary atomizing head provided on a front side of the air motor to be rotatable by the air motor, external electrode units provided in a periphery of the rotary atomizing head, and a high-voltage applying unit that applies a high voltage to the external electrode units to indirectly charge paint particles atomized from the rotary atomizing head with the high voltage. In one embodiment of the disclosed apparatus, a shaping air ring is provided with first and second air spout holes wherein the shaping air ring forms part of a ground. The shaping air ring is formed in a cylindrical shape using, for example, a conductive metallic material, and is connected to ground through an air motor. The shaping air ring has an outer peripheral surface and a stepped part formed on a front end part of the shaping air ring by a protruding radial inside part of the shaping air ring.
In this embodiment, a plurality of groove parts are formed on the outer peripheral surface of the shaping air ring to mount an adaptor thereto. The plurality of groove parts are arranged to be spaced by equal intervals in the circumferential direction, whereby the stepped part is formed on the front end part of the shaping air ring by the protruding radial inside part thereof to the forward side.
The cited shaping air ring is provided with first air spout holes and second air spout holes formed therein. The first air spout holes are arranged closer to a radial inside projecting part than the stepped part of the shaping air ring and are provided along a paint releasing edge of the rotary atomizing head. These first air spout holes are arranged to line up annularly. Each of the first air spout holes is communicated with a first air passage and first shaping air is supplied to each of the first air spout holes and the air spout holes spout the first shaping air to the vicinity of the paint releasing edge of the rotary atomizing head. ('797 patent, col. 6, 1. 17, et seq.)
Second air spout holes are formed in the shaping air ring together with the first air spout holes. The second air spout holes are respectively arranged closer to a radial inside than the first air spouts holes and are arranged to line up annularly. Each of the second air spout holes is communicated with a second air passage provided in a housing member. The second shaping air having the same pressure as, or a pressure different from the shaping air, is supplied to the second air spout holes and the second air spout holes spout the second shaping air to the back surface of the rotary atomizing head. The first and second shaping air shears liquid paint released from the rotary atomizing head to accelerate formation of paint particles, and shapes an atomizing pattern of paint particles atomized from the rotary atomizing head. The pressure of the first shaping air and the pressure of the second shaping air are adjusted as needed, said to make it possible to change the atomizing pattern to a desired size or shape. ('797 patent, col. 6, 11. 50-57)
In contrast with known prior art methods for controlling the spray pattern produced by rotary atomizers, the invention provided herein controls the applied pattern using primary shaping air directed through primary shaping air nozzles located peripherally adjacent and around the bell cup outer edge and, in addition, providing secondary shaping air directed obliquely of the primary shaping air using secondary shaping air supplied through secondary shaping air nozzles also located peripherally about the outer edge of the bell cup. The secondary air is supplied to the secondary air nozzles by an auxiliary air-driven turbine which, in operation, combines the secondary shaping air and the primary shaping air to provide separate, controllable and adjustable shaping of atomization patterns over wide ranges, thereby producing unique, heretofore unachievable final coatings.